Some very basic questions

[David M]

Once the plate/film is loaded, it’s held in place by being pressed against the edges of the frame. The adaptors simply prevent the flexible film from being pushed out by the spring.
Something has just occurred to me. Do the proper adaptors, with the turned-over edge, move the film backwards by the thickness of the brass?

 

[moggi1964]

Yes, very expensive. I didn’t realise the price was for one.
It does show that they do exist.

Me neither until I looked closely. But as you say. David they are at least out there.

Aluminum sheet does seem like an obvious and significantly cheaper option Ian.